Processing techniques for making integrated circuit semiconductor devices include various steps where the devices are subjected to bombardment by energetic particles such as ions, electrons, and x-rays. Such techniques include, for example, electron beam exposure of resist materials, electron gun metallization, sputter etching, ion implantation, and reactive plasma etching. These techniques cause radiation damage to the semiconductor crystal and insulating layer structure which may result in a deterioration of the electrical properties of the semiconductor devices. Metal-insulator-silicon (MIS) capacitors and field effect transistors are especially sensitive to this type of damage with the formation of fast surface states, slow states, and fixed charges. Heretofore, thermal annealing has been employed to remove the effects of radiation damage. In metal-oxide-semiconductor (MOS) structures, both fast surface states and fixed charge can be removed in about 30 minutes at temperatures of 400.degree. C. In order to anneal out slow states, a higher temperature of about 450.degree. C is sometimes needed. For FET type metal-nitride-oxide-semiconductor (MNOS) structures, even a 60 minute thermal anneal at 450.degree. C may not be sufficient to remove all of the radiation effects generated by electron beam irradiation. Furthermore, the temperature and the time duration of the thermal annealing process may cause damage to both high density FET circuits and shallowly diffused junctions. For thick nitride layer MNOS structures, the thermal annealing process, is usually only partially effective in recovering the electrical properties.
Another annealing method is the photon or ultraviolet annealing technique. In this technique, the irradiated oxide or nitride-oxide film on a semiconductor wafer is illuminated at room temperature under UV light (.gtoreq.4 eV). This technique, however, does not remove fast surface states or slow states and cannot be used after gate metallization.
Radiation annealing has also been used to a lesser extent than the thermal and photon techniques. It has been observed that electron bombardment of slightly negatively biased MIS devices, which were initially bombarded under positive bias, will anneal out the effects of the initial radiation to a certain extent. U.S. Pat. No. 3,533,857 describes an ion-irradiation damage crystal restoration technique using a combination of heat and ion-irradiation.
Post oxidation, thermal annealing of thermally grown FET gate oxide using a RF heated susceptor to heat the semiconductor wafers is described in IBM TDB, Volume 18, No. 3, page 753 Aug. 1975. This technique maintains cold furnace walls which act to reduce mobile and fixed charges by gettering sodium ions in a neutral or forming gas atmosphere at atmospheric pressure. This process results in heating the wafers to temperatures of 750.degree. to 900.degree. C and, accordingly, could not be used after metallization. It is also believed to be the source of generation of fast surface states.
An annealing technique has now been found which is fast, effective, and which does not require heating the structures to temperatures which would cause physical or chemical damage.